Mobile metal adatoms on single layer, bilayer and trilayer graphene: an ab initio study correlated with experimental electron microscopy data

The plane-wave density functional theory code CASTEP was used with the Tkatchenko-Scheffler van der Waals correction scheme and the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA PBE) to calculate the binding energy of Au, Cr, and Al atoms on the armchair and zigzag edge binding sites of monolayer graphene, and at the high-symmetry adsorption sites of single layer, bilayer, and trilayer graphene. All edge site binding energies were found to be substantially higher than the adsorption energies for all metals. The adatom migration activation barriers for the lowest energy migration paths on pristine monolayer, bilayer, and trilayer graphene were then calculated and found to be smaller than or within an order of magnitude of kBT at room temperature, implying very high mobility for all adatoms studied. This suggests that metal atoms evaporated onto graphene samples quickly migrate across the lattice and bind to the energetically favorable edge sites before being characterized in the microscope. We then prove this notion for Al and Au on graphene with scanning transmission electron microscopy (STEM) images showing that these atoms are observed exclusively at edge sites, and also hydrocarbon-contaminated regions, where the pristine regions of the lattice are completely devoid of adatoms. Additionally, we review the issue of fixing selected atomic positions during geometry optimization calculations for graphene/adatom systems and suggest a guiding principle for future studies

Predicted suppression of the superconducting transition of new high-pressure yttrium phases with increasing pressure from first-principles calculations

Structure searches for new high-pressure phases of Y metal have been performed by using evolutionary algorithms in conjunction with a first-principles, pseudopotential plane-wave method based on density functional theory. The oF16-Fddd and hP3-P3 121 phases are predicted to be energetically favorable at pressures over 97 GPa. These two phases are shown to be dynamically stable by computing their phonon dispersions. We thus propose that oF16-Fddd and hP3-P3 121 are the most probable crystal structures Y may take in the 97-206 GPa range. The superconducting critical temperatures (T c) of the new phases are estimated using the Allen-Dynes formula. The T c is predicted to decrease with increasing pressure over about 100 GPa, in sharp contrast to its observed monotonic increase under lower pressure. The electronic origins of the stabilities of the proposed high-pressure phases have also been investigated.published_or_final_versio

Improved hanger design for robustness of through-arch bridges

Hangers in through arch bridges are important components since they suspend the entire bridge deck from the arch ribs. Local damage at a hanger may lead to subsequent damage of various components in the vicinity or even progressive collapse of the bridge. After reviewing the conventional design of double-hangers in through arch bridges, this paper puts forward a new design approach. The suitability and robustness of this new approach are then verified by numerical simulation of a real bridge. The impact effects induced by local fracture of a hanger on the other structural members are then simulated by dynamic time-history analyses. The new approach of hanger design is shown to improve the structural robustness. In particular, when one or more hangers are damaged thereby causing local failure, the through arch bridge will not be endangered and will still maintain reasonable overall load-carrying capacity so that the necessary emergency measures can be taken.published_or_final_versio

Improved estimation of clock offset in sensor networks

Clock synchronization is an important issue for the design of a network composed of small sensor nodes. Based on the two-way timing message exchange mechanism and assuming an exponential network delay distribution, many analytical results have been presented in the literature by applying the techniques from statistical signal processing. This paper derives the minimum variance unbiased estimator for the clock offset for both symmetric and asymmetric exponential delay cases. For the asymmetric delays, it is shown to be a function of both the minimum and the mean link delays. This result is a very significant contribution since only the minimum link delay observations have been used to estimate the clock offset in the past. For the symmetric case, it is shown to coincide with the maximum likelihood estimator. In addition, the result is also applicable to clock synchronization problem in general computer networks. ©2009 IEEE.published_or_final_versionThe IEEE International Conference on Communications (ICC 2009), Dresden, Germany, 14-18 June 2009. In Proceedings of IEEE ICC, 2009, p. 1-

A cross-cultural investigation into students' evaluation of university teaching

This study uses the applicability paradigm of Marsh (1981) to examine the validity of two evaluation instruments and their underlying model of teaching effectiveness across seven countries with diverse cultures and higher education systems. The results from the seven studies support the reliability, appropriateness, and to some degree convergent and discriminant validities of the two instruments. Similar patterns of item salience and discrimination between good and poor lecturers are also obtained. Hence, the similarity of the results from diverse academic settings generally lends support to the applicability and the cross-cultural validity of these two instruments and their underlying model of teaching. In addition, the finding that Hong Kong, Taiwan, and China are each relatively more similar to the West than among themselves may reflect the fact that their higher education systems are to a certain extent modeled after those of the West.published_or_final_versio

An unusual median nerve formation; A case report and literature review

The Median nerve anatomical variation is commonly encountered. During the dissection of about 65 years of formalin-fixed male cadaver at the  Department of Human Anatomy at National University Faculty of Medicine for undergraduate students in 2016-2017, the left upper limb showed that the  median nerve was formed by the union of the three roots. However, the third root arose from the musculocutaneous nerve inside the coracobrachialis  muscle, perforating the lower part of the muscle and joining the median nerve at the middle of the arm region. Knowledge of these variations is useful  clinically, especially when evaluating symptoms of upper limb trauma, and it is also useful when performing surgical approaches.&nbsp

Co-benefits of greenhouse gas mitigation: A review and classification by type, mitigation sector, and geography

The perceived inability of climate change mitigation goals alone to mobilize sufficient climate change mitigation efforts has, among other factors, led to growing research on the co-benefits of reducing greenhouse gas (GHG) emissions. This study conducts a systematic review (SR) of the literature on the co-benefits of mitigating GHG emissions resulting in 1554 papers. We analyze these papers using bibliometric analysis, including a keyword co-occurrence analysis. We then iteratively develop and present a typology of co-benefits, mitigation sectors, geographic scope, and methods based on the manual double coding of the papers resulting from the SR. We find that the co-benefits from GHG mitigation that have received the largest attention of researchers are impacts on ecosystems, economic activity, health, air pollution, and resource efficiency. The co-benefits that have received the least attention include the impacts on conflict and disaster resilience, poverty alleviation (or exacerbation), energy security, technological spillovers and innovation, and food security. Most research has investigated co-benefits from GHG mitigation in the agriculture, forestry and other land use (AFOLU), electricity, transport, and residential sectors, with the industrial sector being the subject of significantly less research. The largest number of co-benefits publications provide analysis at a global level, with relatively few studies providing local (city) level analysis or studying co-benefits in Oceanian or African contexts. Finally, science and engineering methods, in contrast to economic or social science methods, are the methods most commonly employed in co-benefits papers. We conclude that given the potential mobilizing power of understudied co-benefits (e.g. poverty alleviation) and local impacts, the magnitude of GHG emissions from the industrial sector, and the fact that Africa and South America are likely to be severely affected by climate change, there is an opportunity for the research community to fill these gaps

A note on isoparametric polynomials

We show that any homogeneous polynomial solution of |\nabla F(x)|^2=m^2|x|^(2m-2), m>1, is either a radially symmetric polynomial F(x)=\pm |x|^m (for even m's) or it is a composition of a Chebychev polynomial and a Cartan-M\"unzner polynomial.Comment: 6 page